[Rmt] AD Evaluation comments on draft-ietf-rmt-bb-tfmcc-06
Magnus Westerlund <magnus.westerlund@ericsson.com> Wed, 05 April 2006 11:13 UTC
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Date: Wed, 05 Apr 2006 13:13:05 +0200
From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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Subject: [Rmt] AD Evaluation comments on draft-ietf-rmt-bb-tfmcc-06
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Hi, I have done an AD evaluation of the draft and found a few things I like to have clarified. Depending on the answer it might be necessary to update the draft. 1. Section 1.3: "TFMCC inherently works with all types of networks, including LANs, WANs, Intranets, the Internet, asymmetric networks, wireless networks, and satellite networks." I reacted to the word "all" here. I think it needs a clarification that it is for all networks that enables bi-directional traffic. Could this be fixed in the text? 2. Section 1.3, last paragraph: "TFMCC is designed for applications that use a fixed packet size, and vary their sending rate in packets per second in response to congestion. Some audio applications require a fixed interval of time between packets and vary their packet size instead of their packet rate in response to congestion. The congestion control mechanism in this document cannot be used by those applications." Here my issue is with "Some audio applications require ...". I would like to change this to "Some applications, e.g. those using audio, may require ...". The problem is more encompassing than only audio, audio is however an good example. 3. Section 2.2.1, the ts_r in data packets. I think this section is missing the addition of the delay between receiving the feedback packet with the ts_r and the transmission of ts_r' in the sender to receiver path. 4. I also think the usage of ts_r and ts_i is make a bit unclear by not separating the different instances of the timers. If I understand the RTT measurements loops there are two one for the sender and one for each receiver. < ts_d > ts_i ts_now ts_i2 ts_r' \ ^ \ \ / \ \ / \ V / V t_now ts_r t_now2 ts_i' < tr_d > The sender loop as I understand it starts with the first message containing ts_i. The receiver does a receiver timestamp on the arrival t_now. Then when sending feedback it calculates ts_i'= ts_i + ts_r-t_now This I think is understandable from the text. And following from that the sender's measurement of RTT will be R_r = ts_now - ts_i'. The receivers measurement loop is similar but uses ts_r which is the local clock value of when the feedback messages is going to be sent. According to issue 3 above there doesn't seem to be any indication that ts_r' is ts_r + ts_d, where ts_d is ts_i2-ts_now. The receivers makes it RTT calculation R_sample = t_now2 - ts_r'. From this I have the following questions: A. Was it intentional to ignore ts_d? If not please clarify that the sender should create a ts_r' when sending the value. B. I think one should maybe clarify that there is a ts_now and tr_now as they are different clocks. Now the same variable is used in both chapters which is a bit confusing. C. Clarify which value should be used in the calculations, the ts_r or the ts_r'. 5. Section 3.2 " R_max = max(R_max, s/X + t_gran)" Is it intentional to calculate s/X rather than 8s/X? I react to that the value is bytes divided by bits/s and thus seem to contain a unit error. 6. Section 3.6: I am missing any definition on when slow start may be used. What are the prerequisite for applying the slow start mechanism? 7. Section 4.3.3: In the D_r calculation it seems that the ts_r term should be the ts_r' term instead. Secondly the R' calculation should not contain the ts_i' value, rather ts_i value of the latest received data packet. I think the used notation is creating confusion here. Please clarify this. 8. Section 5.5: Could anyone please explain why the history discounting for I_tot1 does only include the DF_i and not also the DF value? 9. Split references to normative and informational. From my perspective the draft would benefit significantly from clarifying the RTT measurements variables and their usage. When doing that I think a the other more editorial things could also be fixed. Cheers Magnus Westerlund Multimedia Technologies, Ericsson Research EAB/TVA/A ---------------------------------------------------------------------- Ericsson AB | Phone +46 8 4048287 Torshamsgatan 23 | Fax +46 8 7575550 S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com _______________________________________________ Rmt mailing list Rmt@ietf.org https://www1.ietf.org/mailman/listinfo/rmt
- [Rmt] AD Evaluation comments on draft-ietf-rmt-bb… Magnus Westerlund
- [Rmt] Re: AD Evaluation comments on draft-ietf-rm… Magnus Westerlund
- Re: [Rmt] Re: AD Evaluation comments on draft-iet… Magnus Westerlund
- Re: [Rmt] Re: AD Evaluation comments on draft-iet… Magnus Westerlund